FACULTY OF ENGINEERING, TECHNOLOGY & BUILT ENVIRONMENT

SUBJECT CODE & NAME:EM305 ELEMENT OF HEAT TRANSFER

Lecturer Name: Mr. Mohammed Al-GailaniTutor Name: Ms. Nor Fazilah

Student Name:

Student ID:

Semester / Year:January April 2015

EXPERIMENT TITLE:1. Heat Conduction along homogeneous and composite bar.

2. Effect of a Change in Cross-sectional Area and Radial Conduction.

3. Free and Forced Heat Convectiona) Natural Convectionb) Forced Convection

4. Shell and Tube Heat Exchangera) Parallel Flowb) Counter Flowc) Water Temperature Variationd) Flow Rate Variation

5. Concentric Tube Heat Exchanger

EXPERIMENT 1: HEAT CONDUCTION ALONG HOMOGENEOUS AND COMPOSITE BAR

ObjectiveThe goals of the experiment are to investigate Fourier's Law for the linear conduction of heat along a homogeneous bar. Also to study the conduction of heat along a composite bar and evaluate the overall heat transfer coefficient.

Procedures:

1. Insert a brass conductor (25mm diameter) section intermediate section into the linear module and clamp together.2. Turn on the water supply and ensure that water is flowing from the free end of the water pipe to drain. This should be checked at intervals.3. Turn the heater power control knob control panel to the fully anticlockwise position and connect the sensors leads.4. Switch on the power supply and main switch; the digital readouts will be illuminated.5. Turn the heater power control to 40 Watts and allow sufficient time for a steady state condition to be achieved before recording the temperature at all six sensor points and the input power reading on the wattmeter (Q). This procedure can be repeated for other input power between 0 to 40 watts. After each change, sufficient time must be allowed to achieve steady state conditions. 6. Repeat the procedure for composite bar by change the test section with stainless steel section or any other metals (without sensor) into the linear module and clamp together.

Note:i) When assembling the sample between the heater and the cooler take care to match the shallow shoulders in the housings.ii) Ensure that the temperature measurement points are aligned along the longitudinal axis of the unit.

Questions:

1. Plot the temperature profile as a function of distance for both homogeneous and composite bar.2. By using Fouriers Law, calculate the theoretical and actual thermal conductivity for both cases.3. Calculate the Overall Heat Transfer Coefficient, U based on the knowledge of kbrass and kstainless steel and distances x1, x2 and x3.4. Calculate the error between the calculated result and the result obtained during the experiment.

EXPERIMENT 2: EFFECT OF A CHANGE IN CROSS-SECTIONAL AREA AND RADIAL CONDUCTIONObjective: The experiments target are to investigate the effect of a change in the cross-sectional area on the temperature profile along a thermal conductor as well as to examine the temperature profile and determine thermal conductivity of the material resulting from radial conduction through the wall of a cylinder.

Procedure:

Conduct a test with different cross-sectional area of the conductor. Student may vary the heater power between 0 20kWatt. Ensure that the conductor has a good surface contact with the test section. As for the radial conduction, student encourages to vary the heater power between 0 40kWatt.

Questions:

1. Plot the temperature profile as function of distance for both linear and radial conduction. 2. Comment on the trend and slope of the graph.3. Evaluate the thermal conductivity of the material (W/Km) (Radial Conduction).

Linear Conduction Heat Transfer

Fouriers Law states that:

(1)

where,

Q = heat flow rate, [W]

k = thermal conductivity of the material, A = cross-sectional area of the conduction, [m2]dT = changes of temperature between 2 points, [K]dx = changes of displacement between 2 points, [m] From continuity the heat flow rate (Q) is the same for each section of the conductor. Also the thermal conductivity (k) is constant (assuming no change with average temperature of the material).

Hence,

(2) i.e. the temperature gradient is inversely proportional to the cross-sectional area.

AC

AH AC

AC Q

XS XC XH

Figure 1: Temperature distribution with various cross-sectional areas

Radial Conduction Heat Transfer (Cylindrical)

Temperature DistributionTi

To

RiRo

Ri

Ro

Figure 2: Radial temperature distribution

When the inner and outer surfaces of a thick wall cylinder are each at a uniform temperature, heat rows radially through the cylinder wall. From continuity considerations the radial heat flow through successive layers in the wall must be constant if the flow is steady but since the area of successive layers increases with radius, the temperature gradient must decrease with radius.

The amount of heat (Q), which is conducted across the cylinder wall per unit time, is:

(3)

Where,

Q = heat flow rate, [W]L = thickness of the material, [m]

k = thermal conductivity of the material, Ti = inner section temperature, [K]To = outer section temperature, [K]Ro = outer radius, [m]Ri = inner radius, [m]

EXPERIMENT 3: FREE AND FORCED HEAT CONVECTION

Objectives: The experiment aims to illustrate the transfer of heat by convection both naturally and by forced. The parameters that effects the heat transfer are also explore and comparisons between different types of solid surface are made.

PART A Natural ConvectionProcedures:

1. Start up the equipment and remove the fan assembly from the top of the duct and place the flat plate heat exchanger into the test duct. 2. Record the ambient air temperature (tA). Set the heater power control to 20 Watts (clockwise). Allow sufficient time to achieve steady state conditions before noting the heated plate temperature (tH).3. Repeat this procedure at 40, 60 and 80 Watts.4. Replace the flat plate heat exchanger insert by the finned heat exchanger and repeat steps 2 and 3.

PART B Forced ConvectionProcedures:

Design an experiment of forced convection. Student may set the heater power to be 50 Watts and vary the fan speed between 0m/s to 1.5m/s. Replace the flat plate heat exchanger by the finned heat exchanger to vary the experiment.

** Note the ambient air temperature (tA) before set the heater power. Steady state temperatures are required before noting the heated plate temperature (tH).

Questions:

1. Plot a graph of power against temperature (tH-tA). Explain on the graph plotted. (Natural Convection)2. Plot a graph of air velocity against temperature. ( tH tA). Explain on the graph plotted. (Forced Convection)3. Calculate the air mass flow rate, (Given cross sectional area = 0.0144) and the amount of heat transfer,

EXPERIMENT 4: SHELL AND TUBE HEAT EXCHANGERObjectiveThe experiment aims to demonstrate the working principles of industrial heat exchangers. Parallel and counter flow arrangements shall be used and the efficiency of the heat exchanger will be investigated in each case.

PART A Parallel Flow Arrangement

1. Start the circulation of cold water.2. Using the proper selector valve arrangement, set the flow of cold water parallel to the flow of hot water.3. Switch on the main switch and the pump.4. Set the temperature controller to 60C. *Note: You may initially reduce the cold water flow rate to speed up the temperature increase.*5. Set the hot water flow rate to 2 liters/min and the cold water flow rate to 1.5 liters/min.6. Enable to temperature to stabilize before recording the temperatures from T1 to T4.

PART B Counter Flow Heat Exchanger1. Set the temperature controller to 60C, and the hot water flow rate and cold water flow rate to 2 liters/min and 1.5 liters/min respectively.2. Upon reaching steady-state conditions, record the temperature readings from T1 to T4.

PART C Flow Rate Variation1. Use a counter flow set up of the heat exchanger.2. Set the temperature controller to 60C.3. Set the cold water flow rate to 2 liters/min and hot water flow rate as in the table below.PART D Water Temperature Variation1. Use a counter flow set up of the heat exchanger.2. Set both the cold and hot water flow rate to 2 liters/min.3. Vary the hot water temperatures to 65C, 60C, 55C and 50C.4. Upon reaching steady state conditions at each temperature setting, record the temperatures of T1 to T4.

*Please show sample calculation

EXPERIMENT 5: CONCENTRIC TUBE HEAT EXCHANGERObjectiveThe experiment aims to demonstrate the working principles of industrial heat exchangers. Parallel and counter flow arrangements shall be used and the efficiency of the heat exchanger will be investigated in each case.

ProceduresDesign an experiment to find the best efficiency of parallel and counter flow arrangement of concentric heat exchanger. Use previous experiment as guiding. Noted that, temperature readings are from T1 to T6.

*Please show sample calculation

SUMMARY OF THEORY:

Power emitted = Qh h Cph (THin - THout) Power absorbed = QC C CpC (TCin TCout)

Power lost = power emitted - power absorbed

System efficiency, =

Log mean temperature difference, tm = For parallel flow : For counter flow :

Overall heat transfer coefficient, U = where, area = Surface area of contact= p x ODinner tube x Length x tube count= (3.142 x 0.0032 x 0.508) m x 55= 0.281 m - Shell and Tube Heat Exchanger

where, area = Surface area of contact = p x ODinner pipe x Length = (3.142 x 0.015 x 1.36) m = 0.0641 m - Concentric Heat Exchanger

Temperature efficiencies of the heat exchanger are:

a) for the cold medium

C =

b) for the hot medium

H =

c) mean temperature efficiency

mean =